CVE-2020-3572: Cisco Adaptive Security Appliance

High severity, CVSS 8.6. EPSS: 1.8% chance of exploitation in the next 30 days.

A vulnerability in the SSL/TLS session handler of Cisco Adaptive Security Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition on an affected device. The vulnerability is due to a memory leak when closing SSL/TLS connections in a specific state. An attacker could exploit this vulnerability by establishing several SSL/TLS sessions and ensuring they are closed under certain conditions. A successful exploit could allow the attacker to exhaust memory resources in the affected device, which would prevent it from processing new SSL/TLS connections, resulting in a DoS. Manual intervention is required to recover an affected device.

Affected products

• Cisco Adaptive Security Appliance: before 9.6 (fixed in 9.6)
• Cisco Adaptive Security Appliance Software: from 9.8.0, before 9.8.4.26 (fixed in 9.8.4.26); from 9.9.0, before 9.9.2.80 (fixed in 9.9.2.80); from 9.10.0, before 9.10.1.44 (fixed in 9.10.1.44); from 9.12.0, before 9.12.4.4 (fixed in 9.12.4.4); from 9.13.0, before 9.13.1.13 (fixed in 9.13.1.13); from 9.14.0, before 9.14.1.19 (fixed in 9.14.1.19)
• Cisco Secure Firewall Threat Defense: before 6.3.0.6 (fixed in 6.3.0.6); from 6.4.0, before 6.4.0.10 (fixed in 6.4.0.10); from 6.5.0, before 6.6.1 (fixed in 6.6.1)

Published 2020-10-21. Last modified 2026-08-11.